Account quotas are like Kubernetes resource quotas but they are aggregated across namespaces, i.e. if you specify a limit such as limits.memory: 8Gi, the user can use up to 8Gi of memory across all the spaces owned by the account that the quota is defined for.
Admins can manage account quotas in the "Quotas" tab of each cluster. Users can view a list of all quotas of their accounts as well as of the quotas of the accounts of their teams under "Quotas". Both views also show the current utilization for each quota limit.
Account quotas can be created for any existing cluster account and as part of the process of updating and creating cluster accounts when using the UI.